The monitoring of analyte levels is an important part of numerous types of health diagnostics, such as diabetes care. Such monitoring typically involves using a sensor to detect a concentration level of an analyte in an in vitro or in vivo sample taken from a patient. Analyte sensors may function in various modes, including an amperometric mode, in which a current level that correlates to the analyte concentration in the sample is generated at a working electrode.
Analyte sensors may be employed discretely, for instance, by detecting the analyte concentration level in a single sample taken from the patient (e.g., by a pin-prick or needle), or continuously, by implanting the sensor in the patient for a duration of several days or more. Continuous monitoring offers the potential advantages of detecting certain health conditions that often go undetected by discrete monitoring, and the possibility of providing closed-loop control through immediate treatment of such conditions on an as needed basis. For example, if needed, insulin may be provided immediately to a diabetic patient continually monitored for hypoglycemia using an analyte sensor adapted to detect glucose levels.
Conventional analyte sensors used for continuous monitoring are typically formed from substrates (e.g., tantalum) that may have disadvantageous mechanical properties for manufacturing purposes or continuous monitoring applications. For example, tantalum substrates have low tensile strength, making it difficult to fabricate tantalum sensors with small dimensions (e.g., below a 350 micron diameter); thus, it may be difficult to fabricate sensors using conventional substrates at a size sufficiently small to avoid pain and/or discomfort during insertion and/or implantation.
Tantalum substrates are also susceptible to embrittlement if exposed to hydrogen. For example, when tantalum is used as a substrate material of an analyte sensor, care should be taken to completely coat the working electrode regions of the sensor with platinum or another anode material to avoid direct contact between the chemical reactants which produce current at the working electrode regions and the underlying tantalum substrate. As platinum and similar materials are expensive, these measures add considerably to the expense of conventional analyte sensors.
It would therefore be beneficial to provide an analyte sensor that has both robust mechanical properties and suitable electrical properties adapted for both in vivo and in vitro use.